1. Unit of Hematology, Istituto Giannina Gaslini, Istituto di Ricovero e Cura a Carattere Scientifico (IRCCS), Genoa, Italy;
2. Unit of Paediatric Oncology and Haematology, Santa Maria della Misericordia Hospital, Perugia, Italy; and
3. Biostatistic and Epidemiology Unit, Istituto Giannina Gaslini, IRCCS, Genoa, Italy